Coating process and apparatus



C. T. DAVIS. COATING PROCESS AND APPARATUS. APPLICATION FILED MAY 12,1920.

1,41 6,796. Patented May 23, 1922.

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COATING PROCESS AND APPARATUS.

Application filed May 12,

T 0 all whom it may concern Be it known that I, CHARLES T. DAVIS, acitizen of the United States, and resident of New York city, in thecounty of Kings and State of New York, have invented certain new anduseful Improvements in Coating Processes and Apparatus, of which thefollowing is a specification.

My invention relates to a method and apparatus for applying a coating tosmall articles, and is especially directed to the coating of sucharticles with a substance applied as a liquid and capable of hardeningwith comparative rapidity.

\Vhile my invention is adapted to the coating of a great variety ofarticles, it is especially suitable for applying a coating to medical,pharmaceutical or chemical tablets, pills, capsules, etc., which, forconvenience, will be referred to generally as tablets. Such tablets arenow generally coated by the tumbling process, which requirescomparatively expensive apparatus and is not suited for use with certainsubstances owing to the violent agitation to which the tablets aresubjected. My invention is likewise adapted to the application of tabletcoat ings such as are set forth in my Patent Number 1,335,488.

An object of my invention is to provide a new and improved process ofcoating tablets, and apparatus for carrying out such process, which willapply to a tablet a coating of fluid or viscid material in such a Waythat the tablet will be evenly covered therewith. Another object is toprovide such a process and apparatus capable of rapid and inexpensiveinstallation and operation.

Another well-known method of applying a coating in liquid form whichdries) or hardens in place includes the application of the liquidcoating to the article, ordinarily by immersion of the article therein,and the subsequent location of the article on a suitable support whilethe coating hardens. This method, however, produces an uneven coating,both in thickness and in surface contour. This is caused first by'theengagement of the support with the article, which naturally thins orsqueezes out the coating at such point; and second, by the eifect ofgravity, which causes the fluid to rundown the sides and into thehollows of the article. This unevenness of contour and variationSpecification of Letters Patent.

Patented May as, was.

v1920. Serial No. 330,816.

in the thickness of the coating is in many cases highly objectionable,especially when some portion of the article surface is left entirelyexposed from these causes.

My invention comprises the solution of the problems connected with theapplication to an article of an even, uniform coating which is initiallyapplied in liquid form and which hardens in place, and the avoidance ofthe objections to the tumbling and the stationary hardening processesabove outlined. I have accomplished this result by initially applying asuitable amount of coating to the article, as by immersion, and thenprojecting the article into space, under conditions which tend to hardenthe coating during its flight. With this arrangement, the rough handlingincident to tumbling is avoided, also the unevenness of the coatingcaused by the employment of a support. It also is of such a nature thatonly the simplest of apparatus need be employed, and a thick substantialcoating may be applied evenly and in one quick operation. Furthermore,this process permits the employment of certain coating substances, aswell as certain types of articles, which are. not physically capable ofwithstanding the shocks of tumbling, or the distorting effects of thestationary hardening system.

My improved process is adapted for use with a coating substance whichmay be initially applied to. tablets in fluid or viscid form and whichwill harden with comparative rapidity under proper conditions. Thesephysical characteristics may be inherent in the coating materialemployed; but they may likewise be produced by subjectingsuch materialto special treatment, either for maintaining it in liquid form duringits initial application to the tablets;

for hardening the coating after such initial.

application; or for performing both operations. Various substances arewell known to those skilled in the art which may be rendered fluid andthen hardened by special treatment, and my invention is not restrictedto the specific type of coating substance disclosed, nor to theparticular method vof treating ,it for liquefying and hardening suchsubstance, as other substances and methods of treatment can readily besubstituted therefor by those skilled in the art without exercisinginvention,

One type of coating material suitable for the purpose is normally hardat ordinary temperatures, but is readily liquefied by heating, so thatit may be readily applied to v the tablet in liquid form and hardened bycooling. The various types of Wax afford an example of this material, asthey melt at comparatively low temperatures, 'and can be cooled andhardened very rapidly.'

According to my improved process the coating materialin liquid form isfirst applied to the tablet in any desired way, it being necessary onlythat the requisite amount of such material should adhere to some part ofthe tablet. This step may be performed in various Ways, as .by dippingor immersing the tablet in the coating substance, or by pouring,spraying or otherwise applying such substance directly to the tablet.

After the requisite amount of coating material has been taken up bysuchtablet, I

propel the latter through the air, preferably in such away that it willhave a rotary or gyratory movement during flight. This step serves todistribute the coating evenly over the surface of the tablet, thlseffect 'flight, and as above pointed out, may be accomplished eitherphysically or by chemical action. Where the coating substance isliquefied by heat it may readily be hardened by exposure to cold duringsuch flight, as by projecting it through air ofv asuitable temperature.The same result may beobtained by providing a bath of any desired fluid,such as water, at a suitable temperature, in such a position that thetablet will fall therein at the end of its flight, the

coating being immediately chilled and hardening. Where a chemical resultis relied on,

it may be provided by passing the tablet during flight through asuitable gas, or y projecting it into a bath of the proper chemical.

It is to be understood that while my process is particularly suited forthe applica tion of a coating entirely covering the article, it is notnecessarily restricted thereto as it may be employed with equalefficiency in applying a coating to part of an article by properlyregulating the amount of coat- 3 ing material. initially placed-on-thearticle and the relative speed with which such material is hardened.

One form of apparatus suitable for coatthereby:

tial supply of said coating material, and

means for conducting said-supply into the trough 12, such as an aperture15 in the trough communicating with the coating fluid in the reservoir.When the coating by the application of heat, suitable means is providedfor heating reservoir 14, such provided with inlet and outlet pipes 17for maintaining a supply of heated water therein. This arrangement isparticularly efas a Water jacket 16, which preferably is A "material ismaintained in fluid condition fective in keeping waxy coating material Iat an even temperature.

The tablets falling into trough 12 drop into the coating solutiontherein and are covered I provide means for removing each tablet afterit has been immersed, and for projecting it through the air for asubstantial distance. A convenient arrangement comprises a plurality ofblades or flippers 18 mounted radially'on a rotating shaft 19 and ofsuflicient width to extend across substantiall the entire width oftrough 12. In the pre erredform disclosed, blades 18 are made entirelyof spring material; but

it is apparent that other suitable constructions having resilienttablet-engaging and projecting members may be provided. The feeding oftablets 10 .into trough 12, and the rotation of shaft 19, are preferablytimed so that a tablet will be dropped into the trough in advance ofeach blade 18. As the end-of each-blade moves along thebottom of centthe sides of blades 18, to permit the coating material to flow past saidblades, preventing it from being removed from the trough thereby. Aseach blade rises, it carries a tablet 10 out of the coating solution andup to the top .ofsaid trough at the end opposite to chute 11. At oradjacent this point, I preferably employ suitable means engaging the endportion of said blades to cause them to project the tablet through theair. Where resilient blades or blade parts are employed,'s11ch elementmay con emme construction being such that the continued movement of theblade will carry its resilient end past the abutment with a sudden snap,flipping the tablet supported by such end 1nt0 the air.

In the form disclosed, I have employed a simple trip arm 20 projectingover the edge 0f trough 12 into the path of the ends of blades 18 asufficient distance to engage said ends, but not enough to permit atablet to be crushed between the blade and arm 20. WVhen the parts areproportioned along the lines generally indicated in the drawings,

the tablet 10 will rest upon the upper surface of blade 18 while it isbent by engagement" with trip arm 20, and will be flipped into the airas said blade snaps past the arm upon continued rotation of shaft 19.However, my invention is not restricted to this.

specific arrangement, as obviously many variations in the method ofsupporting and guiding the tablet and of tripping the arm may besubstituted for the one shown by those skilled in the art, withoutdeparting from my invention.

By properly proportioning the parts, the tablet when projected in thismanner will have a rotating or gyratory movement,

.surface 22- to prevent damage to the coating of the tablets. In order.to catch any surplus coating material a drip pan 23 may be providedadjacent arm 20, so located that any overflow from the trough 12', andany spattering as the tablets are flipped through the air, will becaught by the pan and returned to tank 14, pan 23 preferably beingadjacent to or dipping into the water jacket 16 so that the coatingtherein may be maintained in fluid condition. The form of tabletproduced is shown in Figure 3, and consists of the tablet body 10, andan outer coating 24 evenly'spread over the entire surface of said tabletbody.

It will be apparent that numerous variations in the apparatus disclosedmay be made, either for accomplishing substantially the same mechanicalresults, or for adapting the apparatus'to the employment of coatingmaterials other than those liquefied by heat.

It is also'to be understood that while I have disclosed 'a. form ofapparatus which is exclusively adapted to the carrying out of myimproved process, I am fully aware that such process may be carried outby other types of apparatus. In particular, such process is not limitedto the propulsion of the tablets through the air by positive mechanicalimpulse counteracting the effect of gravity, nor is it limited to thedirect engagement of amechanical propelling element with the tablet, asother methods of propulsion are well-known to those skilled in the artand may be applied to such process.

While with certain substances one of the results produced by theprojection into space of the article carrying a liquidcoating is theeven distribution of the coating over the surface while still in fluidcondition, it will be apparent that the coating as applied may besubstantially even; and under such condition it isnot necessary tospread-the coating evenly by means of suitable projection of the articleinto space. \Vhen this is the case, such projection is solely for thepurpose of permitting the coating to harden evenly; and it will beunderstood that the omission of the distributing, step during projectionis within the scope of my invention.

I have employed the term fluid in the claims in its broadest sense, ascovering both liquid and gaseous substances through which the articlemay pass during hardening of the coating.

I claim:

1. A coating process, including the application to pills and likearticles of coating material in liquid form, by immersing the articlesin such material, and the subsequent forcible projection of the articlesthrough space in unsupported flight.

2. A coating process, including the appli-.

ing fluid at a temperature below the liquefying point of said material,the article hemg unsupported during passage through said fluid for asufficient period to permit the hardening of the coatingthroughreductlon of temperature by said fluid.

4. A coating process, including the application to anarticle of acoating material hav ing a point of liquefaction above ordinaryatmospherictemperature. said material being applied to the article whilein liquid form, and the subsequent forcible upward projection of thearticle into air at ordinary temperature, the articleremaining'unsupported in the air for a period sufficient to harden bycooling the coating-material carried thereby.

5. A coating process, including the application to an article of coatingmaterial including wax liquefying at a point substantially aboveordinary atmospheric temperature, the wax being heated and applied inliquid form, and the subsequent forcible upward projection of thearticle through air at ordinary temperature, the article beingunsupported in the air for a period suflicient to permit the coating toharden.-

1 6. A coating apparatus, including means for applying a fluid coatingto the surface of an article, and means for forcibly projectin thecoated article through space. 7. pparatus' for coating pills and likearticles, comprising a coating trough, aflexi- A ble blade arranged tomove articles through ally on the shaft and arranged to move artithetrough, and blade retarding means to cause the blade to flex andforcibly discharge a coated article.

ing liquid coating to the trough, a rotary shaft, flexible impellerblades mounted radicles along the trough bottom through the coatingmedium, and means near the dis charge end of the trough for flexing. andreleasing the blades whereby successive coated articles are forciblyimpelled through air and the coating evenly distributed and hardened.

a rotary shaft, flexible impeller blades mounted radially on the shaftand arranged to move articles along the trough bottom through thecoating medium, and means near the discharge end of the trough forflexing and releasing the blades whereby successive coated articles areforcibly impelled through air,.'and the coating evenly distributed andhardened.

10. Apparatus for coating pills and like articles, comprising a coatingtrough having an arcuate bottom, means for supplying liquid coating tothe trough, means for maintaining the coating in liquid condition, arotary shaft, flexible impeller blades mounted radially on the shaft andarranged to move articles along the trough bottom through the coatingmedium, means near the dlscharge end of the trough for flexing andreleasing the blades whereby successive coated articles are forciblyimpelled through air and the coating evenly distributed and hardened,means for supplying articles successively to the coating trough, meansfor catching the coated articles, and means for receiving coatingmaterial discharged by the blades and returning it for resup'ply to thetrough.

Signed at New York city, in the county of Kings and State of New York,this 11th day of May, A. D. 1920.

0 CHARLES DAVIS.

